Accurate and reproducible patterning, e.g. the removal or deposition of a material, is essential for very large scale integration (“VLSI”) devices. Fine line patterning has become increasingly important as devices shrink. Accordingly, endpoint detection is an indispensable tool for the avoidance of undercutting and loss of feature control.
Prior art methods of endpoint detection for the patterning of layered materials include, but are not limited to, interferometry and optical emission spectroscopy. Both interferometry and optical emission spectroscopy determine patterning endpoint.
FIG. 1 illustrates interferometry, a prior art method. With this prior art method, lasers 102 illuminate a layer 110 undergoing patterning and create an interferometric pattern with the returned lasers 104. From the interferometric pattern, the thickness of the layer 110 is measured. Based upon the measured thickness, patterning endpoint is determined.
Interferometry is problematic because as shown in FIG. 1 interferometry is sensitive to topography variations. As shown in FIG. 1, the layer 110 undulates, which causes returned lasers 104 to bounce unpredictably, which in turn creates random interferometric patterns. Random interferometric patterns cannot be used to reliably determine patterning endpoint.
FIG. 2 illustrates optical emission spectroscopy, another prior art method. Optical emission spectroscopy relies upon the principle that plasma generated materials emit light 206. In FIG. 2, the topmost layer 110 is undergoing thickness alteration. Optical emission spectroscopy monitors the patterning of the layered material 220. The layer material can include, but is not limited to, any combination of a semiconductor, dielectric, or conductor. As shown in FIG. 2, as the set of layers 220 undergoes patterning, a material in the topmost layer 110 emits light 206. A photodetector measures the emitted light 206. Based upon the measured emitted light 206, patterning endpoint is determined.
Optical emission spectroscopy is problematic because some materials do not emit light and optical emission spectroscopy cannot discriminate materials by stoichiometry. For example, silicon nitride is used in both stoichiometric and non-stoichiometric form. When either form of silicon nitride is etched, the emitted light that is monitored by optical emission spectroscopy is the same. Therefore, optical emission spectroscopy cannot discriminate between a layer with stoichiometric versus non-stoichiometric silicon nitride.
These and other deficiencies in the prior art are overcome through the invention.
Therefore, there remains a need in the art for an improved method and system for detection of an endpoint for semiconductors.